Civil transport airplanes are soundproofed and thermically insulated so as to offer maximum comfort to the passengers and aircrew. Insulation mattresses are generally formed of glass wool or another equivalent material and covered with a protective fabric. They are intended to be secured to the metallic structural portions of the aircraft readily resulting in producing heat and vibrations. Their role is to ensure suitable sound and thermic insulation of the plane in relation to the external environment. In other words, they make it possible to protect the passengers and crew from cold temperatures when the plane is flying at high altitudes and noises emanating from the aircraft engine or aerodynamic noises.
The performances of these mattresses are directly linked to their design conception and it is particularly important that they be sealed and that the glass wool constituting them has a homogeneous thickness.
This sound and thermic insulation is nevertheless rarely uniform owing to the various items of equipment traversing this mattress, items such as electric cables or ventilation sheathes and their supports and especially the numerous points for securing this insulation mattress to the fuselage. These fixing points are formed of a large number of gaps affording protection against cold and noise. In fact, the glass wool at the level of these fixing points may allow humidity and condensation water to pass absorbed by said wool.
These sound and thermic insulation mattresses are currently secured to the structure forming a support by means of slugs and fixing washers. The accompanying FIG. 1 shows the methods for preparing and fixing said insulation mattress according to the prior art.
As shown on FIG. 1, the fuselage of the aircraft 1 is covered by a large number of juxtaposed mattresses hereafter denoted as sound and thermic insulation mattresses 3 which are secured to its surface. This mattress is generally made of glass wool. In addition, the fuselage 1 includes at regular intervals sections 5 projecting from its internal surface approximately perpendicular to the latter and denoted hereafter as frames. A single frame is shown on FIG. 1. Each frame 5 is pierced with one orifice 7. The frame 5 is covered on its two faces with an insulation mattress element 3 folded in two. Before being disposed on the frame 5, this mattress has been prepared and pierced so as to facilitate its installation.
This preparation may be effected in two ways shown on both sides of the frame.
As shown in the lower portion of FIG. 1, the insulation mattress 3 is pierced with an orifice 9 having a small diameter and roughly corresponding to the diameter of the fixing slug 11 used for fixing this mattress (for example, 6 mm). The fixing slug 11 is then placed in the orifices 7 and 9 and the mattress is held against the frame 5 by means of two washers 13 forcefully driven onto the slug 11 on both sides of the frame 5 and maintained on the latter by means of the striae 14 of the slug 11.
This type of piercing of the mattress with a small diameter makes it possible to have little or no sound and thermic leaks, but imperviousness of the mattress is not ensured. In fact, the glass wool absorbs condensation water via these orifices 9. Moreover,.the insulation mattress 3 is embrittled in these zones and there may be tears at this location.
The upper portion of FIG. 1 shows a second mode for piercing of the mattress, said mode consisting of piercing an opening 15 with a much larger diameter (for example, about between 38 and 50 mm) and then of laying at the level of this opening 15 two flexible thermoglueing adhesive layers 17 enabling this opening to be bordered. This adhesive may also be reinforced by an excess pitting (not shown on FIG. 1).
The mode for fixing by the slug 11 and the washers 13 is then identical to the one described above. In this case, imperviousness is ensured by the adhesive 17, but the sound and thermic losses caused by the removal of the glass wool are considerable.